Battery energy storage (BESS) sizing calculator

Start from the power you need and for how long. The calculator works back through depth of discharge, round-trip efficiency and end-of-life capacity to the nameplate kWh to ask for, and gives the C-rate the system will run at.

Basis

Nameplate kWh = (kW × hours) ÷ (DoD × efficiency) ÷ end-of-life capacity fraction.

Reference values for planning and comparison. Confirm against the current standard, the purchaser’s specification and the manufacturer’s datasheet before ordering.

Worked example: 2 MW for 4 hours

  1. Energy delivered = 2,000 × 4 = 8,000 kWh.
  2. ÷ (0.90 DoD × 0.88 efficiency) = 10,101 kWh at beginning of life.
  3. ÷ 0.80 end-of-life capacity = 12,626 kWh nameplate, running at 0.158C.

How many kWh battery do I need for 500 kW for 2 hours?

1,000 kWh must be delivered. At 90 % depth of discharge and 88 % efficiency that is about 1,263 kWh at beginning of life, and about 1,578 kWh nameplate if you want the full duration at 80 % end-of-life capacity.

What is C-rate?

C-rate is power divided by energy capacity. A 1 MW, 2 MWh system runs at 0.5C. Lower C-rates usually mean less stress and longer life.

What details are needed for a BESS quotation?

Power (kW/MW), energy (kWh/MWh), use case, AC or DC coupling, grid voltage, cycles per day and site conditions.

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